Supporters of same-sex marriage have successfully framed their opponents as bigots.

Same-sex marriage is probably inevitable in America, whatever the Supreme Court decides. That’s because the public is clearly leaning that way. That the court is even being asked to impose a sweeping social change on the nation is illustrative of another lost battle — the idea that the Supreme Court is not a super-legislature and that nine robed lawyers ought to refrain from imposing their policy preferences on the whole nation.

Even two liberal justices, Ruth Bader Ginsburg and Stephen Breyer, have from time to time expressed caution about the Court’s imposing its will on matters better left up to the people and their elected representatives. It will be interesting to see whether those prudential considerations come into play in their decisions in these cases or whether the desire for a particular outcome overwhelms concerns about the Court’s proper role. Too few Americans recognize this for what it is — a loss of sovereignty.

Champions of same-sex marriage are carrying the day for a number of reasons. (1) The advocacy embedded in popular entertainment such as Modern Family and Brokeback Mountain has been funny, touching, and disarming. (2) Proponents of same-sex marriage appear to be asking for simple justice. (3) Americans would rather stick pins in their eyes than willingly hurt anyone’s feelings. (4) Proponents seem to be embracing the conservative value of marriage.

Beyond all of those factors, though, the most potent argument in the SSM quiver is the race analogy. During oral argument at the Supreme Court, advocates argued (as they have elsewhere) that impairing the right of homosexuals to marry is analogous to proscribing interracial marriage. If that’s true, it’s game, set, and match. If SSM is like interracial marriage, then the only possible motive for opposing it is bigotry.

Liberals slip on this argument like a comfortable sweater. It’s easier to impugn the good faith of your opponents than seriously to grapple with their arguments. Oppose forcing Catholic institutions to distribute free contraceptives? You hate women. Oppose changing the definition of marriage? You hate gays.

To understand opposition to SSM, you must credit that it isn’t about gays, it’s about the institution of marriage, which is the foundation of our civilization. Advocates demand: “How does permitting gays and lesbians to get married hurt your marriage?”

It’s the wrong question. Forty years ago, when illegitimacy was picking up steam in the U.S., conservatives expressed alarm. Liberals responded that traditional families weren’t important — that the only thing that mattered to children was love. Those who argued that the stigmas against divorce and unwed childbearing served important social functions were dismissed as Victorians or bigots. To decry the rise of illegitimacy was to be accused of insensitivity.

That experiment with alternative family structures didn’t go well — as all but the most benighted now acknowledge. The rate of illegitimate births in the U.S. is now 51 percent for women between 20 and 30. It’s a slow-motion disaster for children, for parents, and for the nation.

So how can those who value marriage object to offering its stability to a group that wants to marry? It’s a reasonable question. What we do know is that changing the definition of marriage from a lifelong, exclusive commitment between husbands and wives to an expression of feeling between two adults has not gone well, feelings being mercurial. Enshrining SSM furthers that redefinition.

It may be that when SSM is widely available, same-sex couples will adopt exactly the same standards about commitment and parenthood that male-female couples have traditionally practiced (and that, despite the alarming statistics, most still do). But it’s also possible that gays will bring to marriage very different expectations. Andrew Sullivan, one of the fathers of the SSM movement, has noted that gay unions are more “open” and “flexible” than straight ones. If that’s true, and surveys suggest that it is, will it affect the likelihood that married gay couples will stay together? We don’t know. Will it adversely affect any children in the home? Again, unknown.

Nor do we know whether purposely denying to children of same-sex couples a parent of each sex is damaging. Does having two fathers erase the need for a mother, or vice versa? It’s too early in the history of this experiment to know.

What we do know is that traditional families featuring the lifelong, exclusive commitment of husband and wife are best for children and for society. Gays and lesbians are not responsible for the mess that our culture has made of family life. But perhaps they can understand that resisting its further redefinition is not bigotry but prudence.